The present invention relates to chitinase cDNAs and to a method for their isolation, and more specifically it relates to chitinase cDNAs having a function of conferring plant disease resistance under low temperature, and to a method of isolating the chitinase cDNAs.
In the northern regions, overwintering crops such as barley, forage grasses and wheat must survive subzero temperature (0° C. or below 0° C.) and a long-lasting snow cover condition (0° C. in darkness). However, overwintering crops in such environment are often attacked by snow molds which are a diverse group of psychrophilic parasitic fungi. This biotic stress greatly limits yields and quality of biennial or perennial crops, in the same manner as a low temperature stress will do in the northern region with snow accumulation.
In current winter wheat cultivation, it is necessary to apply a broad-spectrum fungicides before a continuous snow cover for protecting the plant from snow molds infection.
However, it has taken high cost and it has been proved difficult to apply the fungicide at the effective time, because of unstable nature of the start of a snow cover every year.
In view of the above, it has been desired to raise a plant variety having a high disease resistance under tow temperature environment.
Nevertheless, up till now, when using several conventional breeding methods each based on cross-breeding, it has not been possible to raise superior varieties with high resistance, and a long time (many years) is required for raising superior varieties. For this reason, there has been a strong demand for variety improvement by more effective methods such as gene engineering methods.
As a result of repeated diligent research over years aimed at solving the problems described above, the inventors of the present invention have arrived at the following conclusion. Specifically, it has been found that plant disease resistance under low temperature environment is induced by cold acclimation that occurs under a low temperature from autumn through winter (hereunder referred to as “hardening”) and that expression of the three chitinase cDNAs of the invention described hereunder are found during this hardening, with the translation product conferring plant disease resistance through digestion of chitin, one of the major components of fungus cell wall.